Support HEAD method in health endpoints

health.go

@@ -14,9 +14,11 @@ func (app app) healthHandler() func(http.ResponseWriter, *http.Request, loginPar
 	return func(w http.ResponseWriter, r *http.Request, p loginParams) error {
 		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 
-		_, err := w.Write([]byte("ok"))
-		if err != nil {
-			return errors.Wrap(err, "writing response")
+		if r.Method != http.MethodHead {
+			_, err := w.Write([]byte("ok"))
+			if err != nil {
+				return errors.Wrap(err, "writing response")
+			}
 		}
 
 		return nil
@@ -25,7 +27,6 @@ func (app app) healthHandler() func(http.ResponseWriter, *http.Request, loginPar
 
 func (app app) crawlHealthHandler() func(http.ResponseWriter, *http.Request, loginParams) error {
 	return func(w http.ResponseWriter, r *http.Request, p loginParams) error {
-
 		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 
 		lastSampleTime, err := app.ndb.selectLastCrawlTime()
@@ -37,9 +38,11 @@ func (app app) crawlHealthHandler() func(http.ResponseWriter, *http.Request, log
 			return fmt.Errorf("last successful crawl of %d is more than %d minutes ago", lastSampleTime, alertAfterMinutes)
 		}
 
-		_, err = w.Write([]byte("ok"))
-		if err != nil {
-			return errors.Wrap(err, "writing response")
+		if r.Method != http.MethodHead {
+			_, err = w.Write([]byte("ok"))
+			if err != nil {
+				return errors.Wrap(err, "writing response")
+			}
 		}
 
 		return nil

httpserver.go

@@ -70,7 +70,9 @@ func (app app) httpServer(onPanic func(error)) *http.Server {
 	router.GET("/logout", middleware("logout", l, onPanic, app.logoutHandler()))
 
 	router.GET("/health", middleware("health", l, onPanic, app.healthHandler()))
+	router.HEAD("/health", middleware("health", l, onPanic, app.healthHandler()))
 	router.GET("/crawl-health", middleware("crawl-health", l, onPanic, app.crawlHealthHandler()))
+	router.HEAD("/crawl-health", middleware("crawl-health", l, onPanic, app.crawlHealthHandler()))
 
 	server.Handler = app.preRouterMiddleware(router, writeTimeout-100*time.Millisecond)
 

prometheus.go

@@ -26,8 +26,21 @@ var (
 	databaseSizeBytes            *metrics.Gauge
 	databaseFragmentationPercent *metrics.Gauge
 	vacuumOperationsTotal        = metrics.NewCounter(`database_vacuum_operations_total{database="frontpage"}`)
+
+	// Store histograms per route to avoid duplicate registration
+	routeHistograms = make(map[string]*metrics.Histogram)
 )
 
+// getRouteHistogram returns an existing histogram for a route or creates a new one
+func getRouteHistogram(routeName string) *metrics.Histogram {
+	if h, exists := routeHistograms[routeName]; exists {
+		return h
+	}
+	h := metrics.NewHistogram(`requests_duration_seconds{route="` + routeName + `"}`)
+	routeHistograms[routeName] = h
+	return h
+}
+
 func servePrometheusMetrics() func(ctx context.Context) error {
 	mux := http.NewServeMux()
 
@@ -51,15 +64,20 @@ func servePrometheusMetrics() func(ctx context.Context) error {
 }
 
 func prometheusMiddleware[P any](routeName string, h httperror.XHandler[P]) httperror.XHandlerFunc[P] {
-	// Register summary with a single label.
-	requestDuration := metrics.NewHistogram(`requests_duration_seconds{route="` + routeName + `"}`)
+	requestDuration := getRouteHistogram(routeName)
 
 	return func(w http.ResponseWriter, r *http.Request, p P) error {
-		startTime := time.Now()
-		defer requestDuration.UpdateDuration(startTime)
+		var startTime time.Time
+		if r.Method != http.MethodHead {
+			startTime = time.Now()
+		}
 
 		err := h.Serve(w, r, p)
 
+		if r.Method != http.MethodHead {
+			requestDuration.UpdateDuration(startTime)
+		}
+
 		return err
 	}
 }